OP here. I'm amazed by the number of responses to this thread. I didn't expect it. Thanks for the tips, too.
I do feel that my original point is getting lost. I wasn't really looking for an explanation of retail economics, nor for encouragement to buy online.
My point (poorly expressed) was: I see these various strings touted on a daily or hourly basis on TB. Why do I NEVER see them in a big store? I guess the obvious answer is that the number of people who like, say, Ernie Ball Cobalt Flats is in reality much, much smaller than TB leads one to believe. If 100 of us like them, that looks like multitudes.
I know, grumpy old man that I am, that most people buy online now. But to NEVER see these strings in a store?